A valve for use in an automobile internal combustion engine includes a valve stem that interconnects a valve head and a valve tip. The valve stem reciprocates at high speeds and high temperatures within a valve guide. The valve stem can be subjected to frictional wear such that galling or abrasion can occur between the valve stem and the valve guide. “Galling” is defined as an action approaching cold welding that causes adjacent surfaces to have a aggravated by increased engine speeds and operating temperatures as well as decreased availability of lubrication to the valve stem.
Valve stems are typically plated with a chromium coating to decrease the frictional wear between the valve stem and the valve guide. Chromium coatings have a lower coefficient of friction than the base material of the valve. When a chromium coating is applied to a valve stem, it is generally hard and includes micro-cracks. The micro-cracks reduce the residual tensile stress within the chromium coating and help support an oil film along the valve stem.
An engine valve is plated with chromium using a plating apparatus that can selectively plate the valve stem without plating the valve head and valve tip. Examples of plating apparatuses that can be used to selectively plate the valve stem are a rack type plater and a finger type plater.
The valve head and the valve tip are not plated with a chromium coating because a chromium coating tends to reduce the fatigue life of the base material that is plated. Accordingly, a chromium coating is limited to the valve stem in order to minimize the adverse affects of the chromium coating.